A read channel integrated circuit (IC) is one of the core electronic components in a modern hard disk drive. In a magnetic recording system, for example, a read channel converts and encodes data to enable magnetic recording heads to write data to a magnetic medium and to then read back the data accurately. The magnetic media in a magnetic recording system have a number of tracks and each track comprises “read” sectors, with “servo” sectors embedded between the read sectors. The information recorded in the servo sectors helps to position a magnetic recording head so that the user information stored in the read sectors can be retrieved properly.
The servo and read sectors both typically begin with the same known preamble pattern. The read preamble is followed by a read address mark and encoded user data. The servo preamble is followed by a servo address mark and various servo data, including a repeatable run out (RRO) data field that compensates for known errors due to inaccurate spindle centers on the disks. The RRO data field typically comprises an RRO synchronization pattern that is often referred to as an RRO address mark (RROAM), followed by additional RRO data.
When the magnetic hard disk is not spinning exactly at the center, the magnetic recording head will observe an elliptical track rather than a circular track. Flaw scan circuits are typically used to determine the quality of the RRO data that is read from the magnetic media. Existing flaw scan circuits identify low quality samples entering a data detector in a magnetic recording system and set a flag when the number of low quality samples exceeds a specified threshold. The flaw scan circuit will typically begin counting the number of low quality samples after detecting the RRO address mark. When the RRO address mark is missed and a false RRO address mark pattern is later detected due to noise, however, the flaw scan circuit may not properly count the low quality samples. For example, if the false RRO address mark is found towards the end of a servo processing gate, an insufficient number of low quality samples will be captured to set the flag.
A need therefore exists for improved flaw scan circuits for repeatable run out data.